What I did after I got my engine was to drill a hole through the prop I was going to use just a tad under-size using a drill press. Then used a adjustable reamer in drill press to get a slip fit onto the prop shaft. When you make your drilling jig, I made the back side of the jig to fit tight into the prop. Also knurled the outer surface to be able to remove it. You can use the prop washer like TOM said to locate the holes or use a math formula....wich I cannot describe that well. Capt,n